Coexistence of a normal-rate physical layer and a low-rate physical layer in a wireless network

ABSTRACT

A system including a midamble detection module and a processing module. The midamble detection module is configured to detect a midamble of a packet transmitted via a channel, where the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, where the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, where the midamble includes (i) a second short training field and (ii) a second long training field, and where the midamble follows the preamble and is between two or more of the data fields. The processing module is configured to determine that the channel is busy in response to detecting the midamble in the packet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/595,821 filed on Feb. 7, 2012.

This application is related to U.S. Provisional Application No. 61/508,474 filed on Jul. 15, 2011 and U.S. Provisional Application No. 61/528,660 filed on Aug. 29, 2011. This application is also related to U.S. patent application Ser. No. 12/841,772 filed on Jul. 22, 2010, which claims the benefit of U.S. Provisional Application No. 61/228,084 filed on Jul. 23, 2009. This application is also related to U.S. Provisional Application No. 61/486,713, filed on May 16, 2011.

The disclosures of the applications referenced above are incorporated herein by reference in their entirety.

FIELD

The present disclosure relates generally to wireless communication systems and more particularly to coexistence of a normal-rate physical layer and a low-rate physical layer in a wireless network.

BACKGROUND

The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Institute of Electrical and Electronics Engineers (IEEE) has developed standards for wireless local area networks (WLANs). Some of the standards, generally denoted as 802.1x, specify operating parameters including frequency bands, modulation and coding schemes, data rates, and packet formats for WLANs.

To provide high data rates, most WLANs operate in high-frequency bands. For example, WLANs compliant with 802.11a/b/g/n/ac/ad standards operate in 2.4 GHz, 5 GHz, or 60 GHz frequency bands and provide data rates ranging from 11 Mbps to more than 1 Gbps. The range of these WLANs is relatively short, however, due to high frequency of operation.

The range of WLANs can be extended by lowering operating frequencies. When the operating frequencies are lowered, however, the data rates also have to be lowered due to low bandwidth of operation. For example, WLANs compliant with 802.11ah and 802.11af standards operate in a sub-1 GHz frequency band and have longer range but lower data rates than WLANs compliant with 802.11a/b/g/n/ac/ad standards since they operate with bandwidth of 1 or 2 MHz.

SUMMARY

A system comprises a first preamble generation module, a second preamble generation module, and a packet generation module. The first preamble generation module is configured to generate a first preamble. The first preamble includes a first training field to train receivers operating at a first data rate. The second preamble generation module is configured to generate a second preamble. The second preamble includes a second training field to train receivers operating at a second data rate. The second data rate is different than the first data rate. The packet generation module is configured to generate a packet. The packet includes the second preamble followed by the first preamble in response to the packet being transmitted at the first data rate, or the first preamble followed by the second preamble in response to the packet being transmitted at the second data rate.

In other features, the system further comprises a physical layer module configured to transmit the packet at the first data rate in response to the packet including the second preamble followed by the first preamble.

In other features, the system further comprises a physical layer module configured to transmit the packet at the second data rate in response to the packet including the first preamble followed by the second preamble.

In other features, the system further comprises a first physical layer module configured to transmit the packet at the first data rate in response to the packet including the second preamble followed by the first preamble, and a second physical layer module configured to transmit the packet at the second data rate in response to the packet including the first preamble followed by the second preamble.

In still other features, a receiver comprises a physical layer module and a processing module. The physical layer module is configured to receive a packet via a medium. The packet includes a first preamble followed by a second preamble. The first preamble is generated based on a first data rate. The second preamble is generated based on a second data rate. At least one of the first preamble and the second preamble includes a duration of the packet. The processing module is configured to process (i) the first preamble in response to the receiver operating at the first data rate or (ii) the second preamble in response to the receiver operating at the second data rate, and determine whether to defer accessing the medium for the duration of the packet based on the processing of the first preamble or the second preamble.

In other features, the first preamble includes (i) a first training field to train receivers operating at the first data rate and (ii) a first signal field to indicate the duration of the packet, and the processing module is configured to process the first preamble in response to the receiver (i) operating at the first data rate and (ii) training on the first training field, and determine the duration of the packet based on the first signal field. The processing module is configured to (i) detect an identifier in the first signal field and (ii) decide not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, the second preamble includes (i) a second training field to train receivers operating at the second data rate and (ii) a second signal field to indicate the duration of the packet, and the processing module is configured to process the second preamble in response to the receiver (i) operating at the second data rate and (ii) training on the second training field, and determine the duration of the packet based on the second signal field. The processing module is configured to (i) detect an identifier in the second signal field and (ii) decide not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, in response to the packet including data generated at the second rate and the receiver being configured to operate at the second rate, the processing module is configured to process the first preamble, determine whether the packet includes data generated at the second rate based on the processing of the first preamble, process the second preamble in response to determining that the packet includes data generated at the second rate, and determine the duration of the packet based on the processing of the second preamble. The processing module is configured to (i) detect an identifier in the second preamble and (ii) decide not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, in response to the packet including data generated at the first rate and the receiver being configured to operate at the first rate and the second rate, the processing module is configured to process the first preamble, determine whether the packet includes data generated at the second rate based on the processing of the first preamble, process the second preamble in response to determining that the packet includes data generated at the second rate, and determine the duration of the packet based on the processing of the second preamble. The processing module is configured to (i) detect an identifier in the second preamble and (ii) decide not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In still other features, a method comprises generating a first preamble, wherein the first preamble includes a first training field to train receivers operating at a first data rate; and generating a second preamble, where the second preamble includes a second training field to train receivers operating at a second data rate, and the second data rate is different than the first data rate. The method further comprises generating a packet, where the packet includes the second preamble followed by the first preamble in response to the packet being transmitted at the first data rate, or the first preamble followed by the second preamble in response to the packet being transmitted at the second data rate.

In other features, the method further comprises transmitting the packet at the first data rate in response to the packet including the second preamble followed by the first preamble.

In other features, the method further comprises transmitting the packet at the second data rate in response to the packet including the first preamble followed by the second preamble.

In other features, the method further comprises transmitting the packet at the first data rate in response to the packet including the second preamble followed by the first preamble, and transmitting the packet at the second data rate in response to the packet including the first preamble followed by the second preamble.

In still other features, a method comprises receiving a packet at a receiver via a medium, where the packet includes a first preamble followed by a second preamble, the first preamble is generated based on a first data rate, the second preamble is generated based on a second data rate, and at least one of the first preamble and the second preamble includes a duration of the packet. The method further comprises processing (i) the first preamble in response to the receiver operating at the first data rate or (ii) the second preamble in response to the receiver operating at the second data rate, and determining whether to defer accessing the medium for the duration of the packet based on the processing of the first preamble or the second preamble.

In other features, the first preamble includes (i) a first training field to train receivers operating at the first data rate and (ii) a first signal field to indicate the duration of the packet, and the method further comprises processing the first preamble in response to the receiver (i) operating at the first data rate and (ii) training on the first training field, and determining the duration of the packet based on the first signal field. The method further comprises detecting an identifier in the first signal field, and deciding not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, the second preamble includes (i) a second training field to train receivers operating at the second data rate and (ii) a second signal field to indicate the duration of the packet, and the method further comprises processing the second preamble in response to the receiver (i) operating at the second data rate and (ii) training on the second training field, and determining the duration of the packet based on the second signal field. The method further comprises detecting an identifier in the second signal field, and deciding not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, the method further comprises, in response to the packet including data generated at the second rate and the receiver being configured to operate at the second rate, processing the first preamble, determining whether the packet includes data generated at the second rate based on the processing of the first preamble, processing the second preamble in response to determining that the packet includes data generated at the second rate, and determining the duration of the packet based on the processing of the second preamble. The method further comprises detecting an identifier in the second preamble, and deciding not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In other features, the method further comprises, in response to the packet including data generated at the first rate and the receiver being configured to operate at the first rate and the second rate, processing the first preamble, determining whether the packet includes data generated at the second rate based on the processing of the first preamble, processing the second preamble in response to determining that the packet includes data generated at the second rate, and determining the duration of the packet based on the processing of the second preamble. The method further comprises detecting an identifier in the second preamble, and deciding not to access the medium for the duration of the packet in response to the identifier indicating that the packet is not indented for the receiver.

In still other features, an access point comprises a first physical layer module and a second physical layer module. The first physical layer module is configured to communicate at a first data rate via a first sub-channel and a second sub-channel of a channel. The second physical layer module is configured to communicate at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the first data rate is greater than the second data rate. The first physical layer module is configured to receive, from a first client station, a request to reserve the channel for transmitting data from the first client station to the access point at the first data rate, where the request is not received by a second client station configured to transmit data to the access point via the first sub-channel or the second sub-channel at the second rate. In response to the first physical layer module receiving the request from the first client station, the access point is configured to transmit a response to (i) allow the first client station to transmit data at the first data rate via the channel, and (ii) prevent the second client station from transmitting data via the first sub-channel or the second sub-channel at the second rate while the first client station transmits data at the first data rate to the access point via the channel.

In other features, the request includes a ready-to-send frame, where the response includes a clear-to-send frame, and where the first physical layer module and the second physical layer module send the clear-to-send frame.

In other features, the first physical layer module transmits the response prior to the second physical layer module transmitting the response, and the second physical layer module transmits the response subsequent to the first physical layer module transmitting the response; or the second physical layer module transmits the response prior to the first physical layer module transmitting the response, and the first physical layer module transmits the response subsequent to the second physical layer module transmitting the response.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, in response to the first client station receiving the response, the first physical layer module is configured to receive data from the first client station without interference from the second client station.

In still other features, an access point comprises a first physical layer module and a second physical layer module. The first physical layer module is configured to communicate at a first data rate via a first sub-channel and a second sub-channel of a channel. The second physical layer module is configured to communicate at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the first data rate is greater than the second data rate. The second physical layer module is configured to receive, from a first client station, a request to reserve the first sub-channel or the second sub-channel for transmitting data from the first client station to the access point at the second data rate, where the request is not processed by a second client station configured to transmit data to the access point via the channel at the first rate. In response to the second physical layer module receiving the request from the first client station, the access point is configured to transmit a response to (i) allow the first client station to transmit data at the second data rate via the first sub-channel or the second sub-channel, and (ii) prevent the second client station from transmitting data at the first data rate via the channel while the first client station transmits data at the second data rate to the access point via the first sub-channel or the second sub-channel.

In other features, the request includes a ready-to-send frame, where the response includes a clear-to-send frame, and where the first physical layer module and the second physical layer module send the clear-to-send frame.

In other features, the first physical layer module transmits the response prior to the second physical layer module transmitting the response, and the second physical layer module transmits the response subsequent to the first physical layer module transmitting the response; or the second physical layer module transmits the response prior to the first physical layer module transmitting the response, and the first physical layer module transmits the response subsequent to the second physical layer module transmitting the response.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, in response to the first client station receiving the response, the second physical layer module is configured to receive data from the first client station without interference from the second client station.

In still other features, a first client station comprises a first physical layer module and a second physical layer module. The first physical layer module is configured to communicate at a first data rate via a first sub-channel and a second sub-channel of a channel. The second physical layer module is configured to communicate at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the first data rate is greater than the second data rate. The first client station is configured to communicate with an access point associated with a second client station capable of communicating at the first data rate. The first client station is configured to transmit (i) a request to the access point to reserve the channel for transmitting data at the first data rate or to reserve the first sub-channel or the second sub-channel for transmitting data at the second data rate and (ii) data to the access point without interference from the second client station, using one of the following: (i) the second physical layer module only, (ii) the first physical layer module and the second physical layer module, (iii) transmission of a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate and includes no payload, and where the second packet is generated at the second data rate and includes payload, or (iv) transmission of the second packet followed by the gap and the first packet.

In other features, a system comprises the first client station and the access point. The access point is configured to transmit a response to (i) allow the first client station to transmit data using the first physical layer module via the channel or using the second physical layer module via the first sub-channel or the second sub-channel and (ii) prevent the second client station from transmitting data via the channel while the first client station transmits data to the access point.

In other features, the access point comprises a third physical layer module and a fourth physical layer module. The third physical layer module is configured to communicate at the first data rate via the first sub-channel and the second sub-channel. The fourth physical layer module is configured to communicate at the second data rate via (i) the first sub-channel or (ii) the second sub-channel. The access point transmits the response using one of the following: (i) the fourth physical layer module only, (ii) the third physical layer module and the fourth physical layer module, (iii) transmission of a third packet followed by the gap and a fourth packet, where the third packet is generated at the first data rate and includes no payload and a preamble, where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point, and where the fourth packet is generated at the second data rate and includes payload, or (iv) transmission of the fourth packet followed by the gap and the third packet.

In still other features, a method comprises communicating at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of an access point and communicating at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the access point, where the first data rate is greater than the second data rate. The method further comprises receiving at the first physical layer module, from a first client station, a request to reserve the channel for transmitting data from the first client station to the access point at the first data rate, where the request is not received by a second client station configured to transmit data to the access point via the first sub-channel or the second sub-channel at the second rate. The method further comprises, in response to the first physical layer module receiving the request from the first client station, transmitting a response from the access point to (i) allow the first client station to transmit data at the first data rate via the channel, and (ii) prevent the second client station from transmitting data via the first sub-channel or the second sub-channel at the second rate while the first client station transmits data at the first data rate to the access point via the channel.

In other features, the request includes a ready-to-send frame, where the response includes a clear-to-send frame, and where the first physical layer module and the second physical layer module send the clear-to-send frame.

In other features, the method further comprises transmitting the response from the first physical layer module prior to the second physical layer module transmitting the response, and transmitting the response from the second physical layer module subsequent to the first physical layer module transmitting the response; or transmitting the response from the second physical layer module prior to the first physical layer module transmitting the response, and transmitting the response from the first physical layer module subsequent to the second physical layer module transmitting the response.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the method further comprises, in response to the first client station receiving the response, receiving data at the first physical layer module from the first client station without interference from the second client station.

In still other features, a method comprises communicating at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of an access point; and communicating at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the access point, where the first data rate is greater than the second data rate. The method further comprises receiving at the second physical layer module, from a first client station, a request to reserve the first sub-channel or the second sub-channel for transmitting data from the first client station to the access point at the second data rate, where the request is not processed by a second client station configured to transmit data to the access point via the channel at the first rate. The method further comprises, in response to the second physical layer module receiving the request from the first client station, transmitting a response from the access point to (i) allow the first client station to transmit data at the second data rate via the first sub-channel or the second sub-channel, and (ii) prevent the second client station from transmitting data at the first data rate via the channel while the first client station transmits data at the second data rate to the access point via the first sub-channel or the second sub-channel.

In other features, the request includes a ready-to-send frame, where the response includes a clear-to-send frame, and where the first physical layer module and the second physical layer module send the clear-to-send frame.

In other features, the method further comprises transmitting the response from the first physical layer module prior to the second physical layer module transmitting the response, and transmitting the response from the second physical layer module subsequent to the first physical layer module transmitting the response; or transmitting the response from the second physical layer module prior to the first physical layer module transmitting the response, and transmitting the response from the first physical layer module subsequent to the second physical layer module transmitting the response.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

In other features, the method further comprises, in response to the first client station receiving the response, receiving data at the second physical layer module from the first client station without interference from the second client station.

In still other features, a method comprises communicating at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of a first client station; and communicating at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the first client station, where the first data rate is greater than the second data rate, and where the first client station is configured to communicate with an access point associated with a second client station capable of communicating at the first data rate. The method further comprises transmitting from the first client station (i) a request to the access point to reserve the channel for transmitting data at the first data rate or to reserve the first sub-channel or the second sub-channel for transmitting data at the second data rate and (ii) data to the access point without interference from the second client station, using one of the following: (i) the second physical layer module only, (ii) the first physical layer module and the second physical layer module, (iii) transmission of a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate and includes no payload, and where the second packet is generated at the second data rate and includes payload, or (iv) transmission of the second packet followed by the gap and the first packet.

In other features, the method further comprises transmitting from the access point a response to (i) allow the first client station to transmit data using the first physical layer module via the channel or using the second physical layer module via the first sub-channel or the second sub-channel and (ii) prevent the second client station from transmitting data via the channel while the first client station transmits data to the access point.

In other features, the method further comprises communicating at the first data rate via the first sub-channel and the second sub-channel using a third physical layer module of the access point; and communicating at the second data rate via (i) the first sub-channel or (ii) the second sub-channel using a fourth physical layer module of the access point. The method further comprises transmitting the response from the access point using one of the following: (i) the fourth physical layer module only, (ii) the third physical layer module and the fourth physical layer module, (iii) transmission of a third packet followed by the gap and a fourth packet, where the third packet is generated at the first data rate and includes no payload and a preamble, where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point, and where the fourth packet is generated at the second data rate and includes payload, or (iv) transmission of the fourth packet followed by the gap and the third packet.

In still other features, a system comprises a physical layer module and a processing module. The physical layer module is configured to communicate at a first data rate via a channel, where the channel includes (i) a first sub-channel and (ii) a second sub-channel of the channel, receive a first packet including a first preamble transmitted at the first data rate via (i) the first sub-channel and (ii) the second sub-channel, and receive a second packet including a second preamble transmitted at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the second data rate is less than the first data rate. The processing module is configured to process (i) the first preamble transmitted at the first data rate and (ii) at least a portion of the second preamble transmitted at the second data rate.

In other features, the processing module is configured to determine that the channel is busy in response to detecting at least the portion of the second preamble transmitted via (i) the first sub-channel or (ii) the second sub-channel.

In other features, the system further comprises an energy detection module configured to detect an energy level in the channel and determine that the channel is busy in response to the energy level being greater than or equal to a predetermined threshold.

In other features, the first preamble includes (i) a first short training field having a first periodicity and (ii) a first remainder, the second preamble includes (i) a second short training field having a second periodicity and (ii) a second remainder, the second periodicity is equal to the first periodicity divided by an integer greater than or equal to one, and the first remainder is different than the second remainder.

In other features, each of the first short training field and the second short training field activates the processing module to process (i) the first preamble transmitted at the first data rate and (ii) at least the portion of the second preamble transmitted at the second data rate.

In other features, the second remainder includes a signal field, and the processing module is configured to process the signal field, determine a duration of the second packet based on processing the signal field, and defer accessing the channel for the duration.

In other features, the second remainder includes (i) a long training field and (ii) a first signal field, and the processing module is configured to process (i) the second short training field and (ii) the long training field. In response to the processing module being unable to process the first signal field, the processing module is configured to defer accessing the channel until the processing module detects a second signal field of the first preamble, the processing module detects a frame sequence to set a network allocation vector, or expiration of a predetermined period corresponding to a duration of (i) the second packet or (ii) a single transmission sequence.

In other features, the processing module is configured to defer accessing the channel for a first predetermined period, access the channel at an end of the first predetermined period, and subsequent to gaining access to the channel at the end of the first predetermined period, access the channel for a second predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle assigned to a device transmitting the second packet. The device accesses the channel during the first predetermined period and does not access the channel during the second predetermined period.

In other features, the system further comprises an energy detection module configured to detect an energy level of the second packet, where the processing module is configured to defer accessing the channel in response to the energy level being greater than or equal to a predetermined threshold.

In other features, the system further comprises an energy detection module configured to detect an energy level of the second packet, where the processing module is configured to defer accessing the channel in response to the energy level being (i) greater than or equal to a predetermined energy detection threshold and (ii) less than or equal to a preamble detection threshold.

In other features, the processing module is configured to defer accessing the channel for a predetermined period unless, prior to expiration of the predetermined period, the processing module detects (i) duration of the first packet or the second packet respectively from a signal field of the first preamble or the second preamble or (ii) network allocation vector duration.

In other features, the second preamble includes a short training field and is transmitted by a device configured to transmit (i) the first preamble via the channel at the first data rate and (ii) the second preamble via the first sub-channel or the second sub-channel at the second data rate, and a length of the short training field is increased in response to a transmission from the device at the second rate failing a plurality of times. The system further comprises an energy detection module configured to detect an energy level of the second packet, where the processing module is configured to defer accessing the channel in response to detecting the short training field having an increased length, or defer accessing the channel in response to (i) the energy level being greater than or equal to a predetermined threshold and (ii) the short training field having the increased length not being detected.

In other features, the system further comprises an energy detection module configured to detect an energy level of the second packet, where the processing module is configured to defer accessing the channel in response to (i) the energy level being greater than or equal to a predetermined threshold and (ii) the second preamble being not detected. Subsequent to gaining access to the channel based on the energy level, the processing module is further configured to (i) access the channel for a first predetermined period, (ii) stop accessing the channel after expiration of the first predetermined period, and (iii) not access the channel for a second predetermined period following the expiration of the first predetermined period, where the first predetermined period and the second predetermined period are based on a predetermined duty cycle.

In still other features, a method comprises communicating at a first data rate via a channel using a physical layer module, where the channel includes (i) a first sub-channel and (ii) a second sub-channel of the channel. The method further comprises receiving, using the physical layer module, a first packet including a first preamble transmitted at the first data rate via (i) the first sub-channel and (ii) the second sub-channel. The method further comprises receiving, using the physical layer module, a second packet including a second preamble transmitted at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the second data rate is less than the first data rate. The method further comprises processing (i) the first preamble transmitted at the first data rate and (ii) at least a portion of the second preamble transmitted at the second data rate.

In other features, the method further comprises determining that the channel is busy in response to detecting at least the portion of the second preamble transmitted via (i) the first sub-channel or (ii) the second sub-channel.

In other features, the method further comprises detecting an energy level in the channel and determining that the channel is busy in response to the energy level being greater than or equal to a predetermined threshold.

In other features, the first preamble includes (i) a first short training field having a first periodicity and (ii) a first remainder, the second preamble includes (i) a second short training field having a second periodicity and (ii) a second remainder, the second periodicity is equal to the first periodicity divided by an integer greater than or equal to one, and the first remainder is different than the second remainder.

In other features, each of the first short training field and the second short training field activates the processing of (i) the first preamble transmitted at the first data rate and (ii) at least a portion of the second preamble transmitted at the second data rate.

In other features, the second remainder includes a signal field, and the method further comprises processing the signal field; determining a duration of the second packet based on processing the signal field; and deferring accessing the channel for the duration.

In other features, the second remainder includes (i) a long training field and (ii) a first signal field, and the method further comprises processing (i) the second short training field and (ii) the long training field. The method further comprises, in response to inability to process the first signal field, deferring accessing the channel until detecting a second signal field of the first preamble, detecting a frame sequence to set a network allocation vector, or expiration of a predetermined period corresponding to a duration of (i) the second packet or (ii) a single transmission sequence.

In other features, the method further comprises deferring accessing the channel for a first predetermined period; accessing the channel at an end of the first predetermined period; and subsequent to gaining access to the channel at the end of the first predetermined period, accessing the channel for a second predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle assigned to a device transmitting the second packet. The device accesses the channel during the first predetermined period and does not access the channel during the second predetermined period.

In other features, the method further comprises detecting an energy level of the second packet; and deferring accessing the channel in response to the energy level being greater than or equal to a predetermined threshold.

In other features, the method further comprises detecting an energy level of the second packet; and deferring accessing the channel in response to the energy level being (i) greater than or equal to a predetermined energy detection threshold and (ii) less than or equal to a preamble detection threshold.

In other features, the method further comprises deferring accessing the channel for a predetermined period unless, prior to expiration of the predetermined period, (i) duration of the first packet or the second packet is detected respectively from a signal field of the first preamble or the second preamble or (ii) network allocation vector duration is detected.

In other features, the second preamble includes a short training field and is transmitted by a device configured to transmit (i) the first preamble via the channel at the first data rate and (ii) the second preamble via the first sub-channel or the second sub-channel at the second data rate, and a length of the short training field is increased in response to a transmission from the device at the second rate failing a plurality of times. The method further comprises detecting an energy level of the second packet; and deferring accessing the channel in response to detecting the short training field having an increased length, or (i) the energy level being greater than or equal to a predetermined threshold and (ii) the short training field having the increased length not being detected.

In other features, the method further comprises detecting an energy level of the second packet and deferring accessing the channel in response to (i) the energy level being greater than or equal to a predetermined threshold and (ii) the second preamble being not detected. The method further comprises, subsequent to gaining access to the channel based on the energy level, (i) accessing the channel for a first predetermined period, (ii) stopping accessing the channel after expiration of the first predetermined period, and (iii) not accessing the channel for a second predetermined period following the expiration of the first predetermined period, where the first predetermined period and the second predetermined period are based on a predetermined duty cycle.

In still other features, a client station comprises a midamble detection module and a processing module. The midamble detection module is configured to detect a midamble of a packet transmitted via a channel, where the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, where the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, where the midamble includes (i) a second short training field and (ii) a second long training field, and where the midamble follows the preamble and is between two or more of the data fields. The processing module is configured to determine that the channel is busy in response to detecting the midamble in the packet.

In other features, in response to the midamble being present in the packet following every predetermined number of data symbols, the client station further comprises a power save module configured to operate the client station in a power save mode for a duration of (i) the predetermined number of data symbols or (ii) a multiple of the predetermined number of data symbols, and to wake up the client station following the duration, where the processing module is configured to determine, subsequent to the client station waking up, that the channel is busy in response to detecting the midamble in the packet.

In other features, in response the midamble not being detected in the packet, the processing module is configured to determine whether the channel is busy in response to detecting the preamble.

In other features, the client station further comprises a physical layer module configured to communicate at a first data rate via (i) a first sub-channel or (ii) a second sub-channel of the channel, where the midamble detection module is configured to detect the midamble in (i) the first sub-channel or (ii) the second sub-channel in response to the midamble being transmitted at a second data rate via (i) the first sub-channel and (ii) the second sub-channel, where the second data rate is greater than the first data rate. The processing module is configured to determine, in response to the midamble being detected in (i) the first sub-channel or (ii) the second sub-channel, that a transmission at the second data rate is ongoing in the channel, and to decide not to access the channel.

In still other features, a method comprises detecting a midamble of a packet transmitted via a channel, where the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, where the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, where the midamble includes (i) a second short training field and (ii) a second long training field, and where the midamble follows the preamble and is between two or more of the data fields. The method further comprises determining that the channel is busy in response to detecting the midamble in the packet.

In other features, in response to the midamble being present in the packet following every predetermined number of data symbols, the method further comprises operating a client station in a power save mode for a duration of (i) the predetermined number of data symbols or (ii) a multiple of the predetermined number of data symbols; waking up the client station following the duration; and determining, subsequent to the client station waking up, that the channel is busy in response to detecting the midamble in the packet.

In other features, the method further comprises, in response the midamble not being detected in the packet, determining whether the channel is busy in response to detecting the preamble.

In other features, the method further comprises communicating at a first data rate via (i) a first sub-channel or (ii) a second sub-channel of the channel using a physical layer module; detecting the midamble in (i) the first sub-channel or (ii) the second sub-channel in response to the midamble being transmitted at a second data rate via (i) the first sub-channel and (ii) the second sub-channel, where the second data rate is greater than the first data rate; and determining, in response to the midamble being detected in (i) the first sub-channel or (ii) the second sub-channel, that a transmission at the second data rate is ongoing in the channel, and deciding not to access the channel.

Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a table depicting examples of use cases including indoor and outdoor networks;

FIG. 2A depicts an example of a packet including a normal-rate preamble;

FIG. 2B depicts an example of a packet including a low-rate preamble;

FIG. 3 is a functional block diagram of a network including an access point and a plurality of client stations;

FIG. 4 depicts an example of a low-rate packet including a normal-rate preamble prepended to a low-rate preamble;

FIG. 5 depicts an example of a normal-rate packet including a low-rate preamble prepended to a normal-rate preamble;

FIG. 6 depicts an example of a packet including a plurality of midambles;

FIG. 7A depicts an example of a plurality of overlapping basic service sets, where the basic service sets include normal-rate physical layer network devices;

FIG. 7B depicts an example of a plurality of overlapping basic service sets, where the basic service sets include normal-rate and low-rate physical layer network devices;

FIG. 8 is a functional block diagram of a network device;

FIG. 9A is a functional block diagram of a network device including a hybrid physical layer that operates at a normal rate and a low-rate;

FIG. 9B is a functional block diagram of a network device including a normal-rate physical layer and a low-rate physical layer;

FIG. 10 is a functional block diagram of a client station capable of performing energy detection;

FIG. 11 is a functional block diagram of a client station capable of detecting midambles;

FIG. 12 is a flowchart of a method for transmitting a packet according to the present disclosure;

FIGS. 13A and 13B depict a flowchart for a method for processing a received packet according to the present disclosure;

FIGS. 14A and 14B depict a flowchart for a method for solving the hidden terminal problem according to the present disclosure;

FIGS. 15A and 15B depict a flowchart for a method for solving the coexistence problems according to the present disclosure;

FIG. 16 depicts a flowchart of a method for solving the coexistence problem according to the present disclosure;

FIGS. 17A-17C depict a flowchart of a method for coexistence of devices having varying capabilities according to the present disclosure; and

FIG. 18 is a flowchart of a method for coexistence of a normal-rate physical layer and a low-rate physical layer in a wireless network using midambles according to the present disclosure.

DESCRIPTION

A physical layer (PHY) device operating at a normal data rate specified by 802.11ah and 802.11af standards is called a normal-rate PHY. A low-rate PHY operates at a data rate lower than the normal data rate and can be used, for example, in long-range WiFi and sensor networks. For example, the low-rate PHY can be used in devices that are compliant with 802.11ah and 802.11af standards and that operate in a sub-1 GHz frequency band. Examples of use cases discussed below indicate that both normal-rate and low-rate PHYs can coexist. That is, a device can include both a normal-rate PHY and a low-rate PHY. Alternatively, a device including only the normal-rate PHY and a device including only the low-rate PHY can coexist in a network.

The present disclosure relates to preamble designs that allow a normal-rate PHY and a low-rate PHY to coexist. Specifically, the preamble designs allow the normal-rate and low-rate PHYs to automatically detect the preambles and to defer (i.e., back off) when the detected preamble is not intended for the detecting device. Accordingly, the preamble designs can minimize interference due to coexistence.

FIG. 1 illustrates examples of use cases including an indoor network and an outdoor network. Use cases 1 a through 1 h include networks comprising sensors and meters. Use cases 2 a, 2 b include networks comprising backhaul sensor and meter data. Use cases 3 a, 3 b include extended range WiFi networks. The networks used in these use cases may be deployed in indoor and/or outdoor environments.

For each network, FIG. 1 shows a transmit range, a data rate, a link budget, a power level, and whether the network includes mobile devices. The link budget indicates robustness of preamble. For example, a high link budget indicates a need for a robust preamble. A low-rate preamble is more robust than a normal-rate preamble since low-rate transmissions can travel longer distances than normal data rate transmissions (hence the robustness). Accordingly, a high link budget indicates a need for a low-rate preamble, which in turn requires using a low-rate PHY that transmits data at a lower than a normal data rate. A normal link budget indicates a need for a normal-rate preamble, which in turn requires using a normal-rate PHY that transmits data at a normal data rate according to the specification. The low-rate and normal-rate PHYs and preambles are discussed below in detail.

The link budget and the data rate requirements of a use case determine whether the devices in the network can use a low-rate PHY and a low-rate preamble or use a normal-rate PHY and a normal-rate preamble. For example, devices in the networks of use cases 1 f and 1 h may use low-rate PHY; devices in the networks of use cases 1 g and 3 a could use normal-rate PHY; devices in the networks of use cases 1 a and 1 d may use low-rate PHY; devices in the networks of use cases 3 a and 3 b could use normal-rate PHY; and so on. Accordingly, both low-rate and normal-rate PHYs can coexist in the indoor and outdoor environment.

An access point (AP) may communicate with devices (stations or STAs) in the networks servicing a plurality of use cases. The AP may transmit and receive data to and from one set of devices using a low-rate PHY and may transmit and receive data to and from another set of devices using a normal-rate PHY. Without preamble detection and deferral, the STAs could interfere with each other's transmissions. The STAs should defer based on preamble detection to minimize interference and to achieve good coexistence. Accordingly, the STAs should support both normal-rate and low-rate preamble formats.

Referring now to FIGS. 2A and 2B, examples of packets including normal-rate and low-rate preambles are shown. In FIG. 2A, an example of a packet 100 including a normal-rate preamble is shown. The packet 100 carries data at a normal data rate specified by the standard and can be called a normal-rate packet. For example only, the normal-rate preamble shown is a Greenfield mode preamble, which does not include a Legacy portion for backward compatibility with Legacy devices. The normal-rate preamble includes a short training field (STF), a long training field (LTF1), signal fields SIG1 and SIG2 (collectively SIG fields), and remaining LTFs for other data streams (e.g., multiple-input multiple-output or MIMO streams). The normal-rate preamble is followed by very high throughput (VHT) data.

A receiver receiving the packet 100 uses the STF of the normal-rate preamble for packet detection, coarse frequency synchronization, and for setting a gain of an automatic gain control (AGC) of the receiver to process the packet 100. The LTFs (e.g., LTF1 and the remaining LTFs) are used for channel estimation and fine frequency synchronization. The SIG fields (e.g., SIG1 and SIG2) are used to indicate to the receiver a set of PHY parameters such as a modulation and coding scheme (MCS) used to modulate the data in the packet 100. Accordingly, the receiver can process the data in the packet 100 based on the normal-rate preamble.

In FIG. 2B, an example of a packet 150 including a low-rate preamble is shown. The packet 150 carries data at a lower rate that the normal rate specified by the standard and can be called a low-rate packet. For example only, the low-rate preamble shown is also a Greenfield mode preamble. The low-rate preamble includes fields having different signatures than the normal-rate preamble. The low-rate preamble includes a low-rate short training field (LR-STF), a low-rate long training field (LR-LTF1), low-rate signal fields LR-SIG1 and LR-SIG2 (collectively LR-SIG fields), and remaining low-rate LTFs (LR-LTFs) for other data streams. The low-rate preamble is followed by VHT data. A receiver receiving the packet 150 uses the fields of the low-rate preamble to process the packet 150 in a manner similar to that described above with reference to packet 100.

Referring now to FIG. 3, an access point (AP) 200 may communicate with stations STA1 202 and STA2 204. Station STA1 202 may be farther from the AP 200 than the station STA2 204. Accordingly, the AP 200 may transmit to the station STA1 202 using a low-rate PHY, and the AP 200 may transmit to the station STA2 204 using a normal-rate PHY. In each packet, one of the SIG fields in the normal-rate and low-rate preambles includes a length/duration field that indicates a length and/or duration of the packet. If a station determines that a packet is not intended for the station, the station does not access the medium (i.e., defers) for the duration indicated in the length/duration field.

Typically, when the AP 200 transmits a packet including the low-rate preamble to the station STA1 202, the station STA2 204 cannot decode the low-rate preamble since the receiver of the station STA2 204, if capable of operating at the normal rate only, does not train using the fields LR-STF, LR-LTF1, and so on of the low-rate preamble. Accordingly, the station STA2 204 cannot decode the LR-SIG fields in the low-rate preamble and cannot defer. Instead, the station STA2 204 attempts to determine whether the packet is intended for the station STA2 204 using energy detection. Deferral based on energy detection, however, is less robust than deferral based on SIG field detection.

Accordingly, the station STA2 204 may attempt to transmit to the AP 200 while the AP 200 is transmitting to the station STA1 202. Similarly, the station STA2 204 may be unable to detect when the station STA1 202 is transmitting using a low-rate PHY to the AP 200. Accordingly, the station STA2 204 may mistake the medium to be free and attempt to transmit to the AP 200 while the station STA1 202 is transmitting to the AP 200 using a low-rate PHY.

Referring now to FIG. 4, a portion of the normal-rate preamble can be prepended to the low-rate preamble when transmitting a packet using a low-rate PHY. For example, the STF, LTF1, and SIG (e.g., SIG1 and/or SIG2) fields of the normal-rate preamble can be prepended to the low-rate preamble when transmitting a packet using a low-rate PHY. Suppose that the AP 200 transmits a packet 250 using a low-rate PHY to the station STA1 202. The packet 250 includes both the low-rate preamble and a portion of the normal-rate preamble prepended to the low-rate preamble as shown.

The station STA2 204 can decode the STF, LTF1, and SIG fields in the portion of the normal-rate preamble. The SIG field in the portion of the normal-rate preamble indicates the duration and/or length of the remainder (i.e., the low-rate preamble and the VHT data portion) of the packet 250. Additionally, the SIG field in the portion of the normal-rate preamble includes an identifier (ID) of the station for which the packet is intended (e.g., ID of the station STA1 202). Accordingly, based on the SIG field in the portion of the normal-rate preamble, the station STA2 204 determines that the packet 250, despite having a portion of the normal-rate preamble, is not intended for the station STA2 204 and defers for the duration indicated by the SIG field.

The station STA1 202 may or may not receive the portion of the normal-rate preamble since the station STA1 202 is farther away from the AP 200 and since the normal-rate preamble is less robust than the low-rate preamble. If the station STA1 202 does not receive the portion of the normal-rate preamble, the station STA1 202 may process the low-rate preamble and process the packet 250 based on the low-rate preamble. For example, the station STA1 202 may defer based on the duration of the remainder of the packet 250 indicated in the LR-SIG field if the packet 250 is not intended for the station STA1 202 but is intended for another station with a low-rate PHY instead.

If the station STA1 202 receives the portion of the normal-rate preamble, the station STA1 202 can determine based on the ID included in the SIG field of the portion of the normal-rate preamble whether the packet 250 is intended for the station STA1 202. Additionally, the SIG field of the portion of the normal-rate preamble can include a bit that indicates whether the packet 250 is a coexistence type packet (i.e., the packet 250 includes a low-rate preamble following the SIG field and is intended for a station with a low-rate PHY). Accordingly, the station STA1 202 can process the low-rate preamble and defer for the duration indicated in the LR-SIG field if the packet 250 is not intended for the station STA1 202.

The station STA1 202 can also transmit packets similar to the packet 250 when transmitting to the AP 200 so that the station STA2 204 can detect, decode, and defer based on the portion of the normal-rate preamble.

Referring now to FIG. 5, a portion of the low-rate preamble can be prepended to the normal-rate preamble when transmitting a packet using a normal-rate PHY. For example, the LR-STF, LR-LTF1, and LR-SIG (e.g., LR-SIG1 and/or LR-SIG2) fields of the low-rate preamble can be prepended to the normal-rate preamble when transmitting a packet using a normal-rate PHY. Suppose that the AP 200 transmits a packet 300 using a normal-rate PHY to the station STA2 204. The packet 300 includes both the normal-rate preamble and a portion of the low-rate preamble prepended to the normal-rate preamble as shown.

The station STA1 201 can decode the LR-STF, LR-LTF1, and LR-SIG fields in the portion of the low-rate preamble. The LR-SIG field in the portion of the low-rate preamble indicates the duration and/or length of the remainder (i.e., the normal-rate preamble and the VHT data portion) of the packet 300. Additionally, the LR-SIG field in the portion of the low-rate preamble may include an ID of the station for which the packet is intended (e.g., ID of the station STA2 204). Accordingly, based on the LR-SIG field in the portion of the low-rate preamble, the station STA1 202 determines that the packet 300, despite having a portion of the low-rate preamble, is not intended for the station STA1 202 and defers for the duration indicated by the LR-SIG field.

The station STA2 204 can process the packet 300 in two ways depending on whether the station STA2 204 supports 1 MHz operation. If the station STA2 204 does not support 1 MHz operation, the station STA2 204 disregards the portion of the low-rate preamble in the packet 300 and processes the normal-rate preamble. The station STA2 204 determines whether to defer for the duration indicated in the SIG field of the normal-rate preamble depending on whether the packet 300 is intended for the station STA2 204 as indicated by an ID in the SIG field.

If the station STA2 204 supports 1 MHz operation, the station STA2 204 processes the portion of the low-rate preamble. The LR-SIG field in the portion of the low-rate preamble may include an ID of the station for which the packet is intended (e.g., ID of the station STA2 204). Additionally, the LR-SIG field in the low-rate preamble may include a bit that indicates whether the packet 300 is a coexistence type packet (i.e., the packet 300 includes a normal-rate preamble following the LR-SIG field and is intended for a station with a normal-rate PHY). Accordingly, based on the LR-SIG field in the low-rate preamble, the station STA2 204 can determine that the packet 300, despite having a portion of the low-rate preamble, is intended for a station having a normal-rate PHY (e.g., the station STA2 204). The station STA2 204 can process the normal-rate preamble and defer for the duration indicated by the SIG field if the packet 300 is not intended for the station STA2 204 but is intended for another station with a normal-rate PHY instead.

Note that the signal fields in both the normal-rate preamble and the low-rate preamble (e.g., the LR-SIG field and the SIG field) may include the ID of the station for which the packet is intended and the duration of the remainder of the packet, where the remainder is a portion of the packet following the respective signal field. Accordingly, when the station STA2 204 supports 1 MHz operation, the station STA2 204 can determine whether to defer based on the ID and duration information in the IR-SIG field or in the SIG field.

The station STA2 204 can also transmit packets similar to the packet 300 when transmitting to the AP 200 so that the station STA1 202 can detect, decode, and defer based on the portion of the low-rate preamble.

Referring again to FIG. 3, coexistence can be managed in other ways. In FIG. 3, if the station STA2 204 uses a normal-rate PHY to communicate with the AP 200, the station STA2 204 becomes a hidden terminal of the station STA1 202. The station STA2 204 may employ various schemes to protect transmissions of the station STA2 204 from interference due to transmissions from the station STA1 202. For example, the schemes can include energy detection, preamble detection, duration detection, and request-to-send/clear-to-send (RTS/CTS) signaling. None of these protective transmissions (e.g., requests transmitted to the AP 200 to reserve medium for transmitting data) from the station STA2 204, however, may reach the station STA1 202 if the station STA2 204 uses a normal-rate PHY and the station STA1 202 uses a low-rate PHY and is far away. Consequently, the station STA1 202 may start transmitting while the station STA2 204 is transmitting.

The hidden terminal issue can be resolved in many ways as follows. Suppose that the AP 200 includes a normal-rate PHY and a low-rate PHY. In a first solution, if the station STA2 204 uses only a normal-rate PHY, the station STA2 204 can initiate protection (i.e., request that the medium be reserved for transmission) by sending a ready-to-send (RTS) frame or a short frame to the AP 200 using the normal PHY. The station STA2 204 can request the AP 200 to respond by sending a clear-to-send (CTS) or a short frame using both the normal-rate PHY and the low-rate PHY. The AP 200 may send a response using the normal-rate PHY and then send the same response using the low-rate PHY. Alternatively, the AP 200 may send a response using the low-rate PHY and then send the same response using the normal-rate PHY.

In a second solution, the AP 200 may respond by transmitting a special hybrid packet including the normal-rate preamble (with protection duration), the low-rate preamble, and a low-rate payload. Alternatively, the AP 200 may respond by transmitting a special hybrid-PHY packet including the low-rate preamble (with protection duration), the normal-rate preamble, and normal-rate payload. The protection duration indicates a duration for which the medium is reserved for the station STA2 204 to transmit data.

In a third solution, the AP 200 may respond by transmitting a normal-rate packet, followed by a gap, followed by a low-rate no-data packet (NDP) (with protection duration). Alternatively, the AP 200 may respond by transmitting a low-rate packet, followed by a gap, followed by a normal-rate packet (with protection duration). The gap may be a short interframe space (SIFS) or a reduced interframe space (RIFS). In some implementations, the NDP may also be sent before the normal-rate packet or the hybrid packet.

In a fourth solution, the AP 200 may transmit the response frame in duplicate (i.e., via each 1 MHz sub-channel of the 2 MHz channel). Note that a low-rate packet is transmitted in a 1 MHz channel while a normal-rate packet is transmitted in a 2 MHz channel (i.e., in two adjacent 1 MHz channels). Once the protection exchange using any of the above schemes is completed, the station STA2 204 can begin a normal-rate session with the AP 200.

Referring again to FIG. 3, the coexistence issue can be described as follows. If the station STA2 204 uses only a normal-rate PHY (or only a low-rate PHY), the station STA2 204 may not detect/decode protection transmissions from the station STA1 202. While energy detection can help, the station STA2 204 cannot perform early packet filtering to save power and cannot decode a duration field (or an equivalent field) for hidden node protection.

The coexistence issue can be resolved in many ways as follows. If the station STA1 202 uses only a low-rate PHY, the station STA1 202 may initiate a protection session by sending a RTS or a short frame to the AP 200 using the low-rate PHY and request the AP 200 to respond using both the normal-rate PHY and the low-rate PHY. Solutions similar to those described above with reference to the hidden terminal issue may be employed. The station STA1 202 uses the protection to reserve a transmit opportunity (TXOP) for a low-rate session.

If the station STA1 202 can use both the normal-rate PHY and the low-rate PHY, the station STA1 202 can initiate protection or send data by using one of the following: the low-rate PHY only, both the low-rate PHY and the normal-rate PHY, a normal-rate NDP followed by a gap followed by a low-rate packet, or a low-rate NDP followed by a gap followed by a normal-rate packet. The AP 200 may respond to protection initiation by using one of the following: the low-rate PHY only, both the low-rate PHY and the normal-rate PHY, a normal-rate NDP followed by a gap followed by a low-rate packet, or a low-rate NDP followed by a gap followed by a normal-rate packet.

Referring now to FIG. 6, coexistence in 802.11ah-based outdoor applications can be resolved using midambles disclosed in U.S. patent application Ser. No. 12/841,772 filed on Jul. 22, 2010, which is incorporated herein by reference in its entirety. The midambles can also be used to determine presence of wireless transmission. In FIG. 6, a packet 350 with midambles is shown. The midambles follow the preamble and are inserted between two or more data fields as shown. The midambles allow a receiver to retrain its channel equalizer for long packets.

The midambles include a short training field (STF) and multiple long training fields (LTFs). A double guard interval (DGI) may be inserted between the STF and the long training symbols (LTSs). Typically, a station performs clear channel assessment (CCA) by trying to detect the preamble or repetition of cyclic prefix (CP). The station can also perform CCA by detecting the midamble. Detecting a midamble is more robust than detecting mid-packet using CP repetition.

A station may perform CCA and defer using midambles as follows. If a station detects the presence of a midamble, the station should determine that the channel is busy and defer transmission. The presence of a midamble can be determined by the presence of STF and one or more LTFs. If the standard specifies midambles after every N symbols, where N is an integer greater than 1, the station can go into power save mode for N (or a multiple of N) symbols, wake up after the N (or a multiple of N) symbols, and try to determine if the packet transmission has ended by detecting a midamble. If no midamble is detected, the station should also perform CCA using preamble detection and guard interval (GI) repetition. A station in a 1 MHz basic service set (BSS) (i.e., a 1 MHz STA) can detect the presence of STF and LTF transmitted in a 2 MHz channel and therefore determine that a 2 MHz transmission is ongoing. The 1 MHz STA using this method will therefore defer.

IEEE 802.11ah defines a normal-rate PHY (NP) and a low-rate PHY (LRP) and may allow two types of devices: single PHY devices having only the normal-rate PHY (NP-only devices) and dual-PHY devices having the normal-rate PHY and the low-rate PHY. A NP-only device can detect partial or whole preamble of LRP transmissions (e.g., the LR-STF, LR-LTF, and/or LR-SIG fields).

The NP-only device sets clear channel access (CCA) status to busy when a partial or whole preamble of a LRP transmission is detected or when a signal energy greater than or equal to a predetermined threshold is detected. The STF of the normal-rate preamble and the LR-STF of the low-rate preamble can be designed with similar structure such that CCA of an NP-only device can be triggered by the LR-STF. For example, the LR-STF can have the same periodicity as the STF. Alternatively, the periodicity of the LR-STF can be 1/N times the periodicity of the STF, where N is an integer greater than 1. Therefore, an autocorrelator in the receiver of the NP-only device is triggered by STF and LR-STF. The remaining portion of the low-rate preamble (i.e., the LR-LTF and the LR-SIG fields) can be different than the corresponding fields of the normal-rate preamble.

Referring now to FIGS. 7A and 7B, examples of coexistence scenarios are shown. In a first scenario shown in FIG. 7A, stations belonging to different basic service sets (BSSs) are shown. For example, one station belonging to a BSS A and two stations belonging to a BSS B are shown. Suppose that stations in BSS B are NP-only devices (i.e., have only normal-rate PHYs or NPs) and that stations in BSS A are dual-PHY devices (i.e., have normal-rate and low-rate PHYs). Large and small circles denote long and short ranges of NP and LRP transmissions from different stations. Suppose further that BBS A and BSS B are NP-overlapping BSSs (NP-OBSSs). That is, when the stations in BSS A and BSS B transmit using NPs, the transmissions can interfere with each other. Suppose also that LRP transmissions from stations in BSS A can be detected by stations in BSS B.

NP transmission and/or protection request from a station in BSS B can reach stations in BSS A and can prevent interference from stations in BSS A at least partially. LRP transmission from a station in BSS A can be detected at least partially by stations in BSS B and may heavily interfere with transmissions from stations in BSS B. Since BSS B is in close proximity to some of the stations in BSS A, the stations in BSS B should respect the detected LRP transmissions from the stations in BSS A and defer their transmissions.

In a second scenario shown in FIG. 7B, for example, one station belonging to a BSS A and one station belonging to a BSS B are shown. Suppose that stations in BSS B are NP-only devices and that stations in BSS A are dual-PHY devices. Suppose further that BSS A and BSS B are not NP-OBSS, but are LRP-overlapping BSSs (LRP-OBSSs) instead. That is, NP transmissions of stations in BSS A and BSS B do not interfere with each other, but LRP transmissions of stations in BSS A can be detected by stations in BSS B.

NP transmission and/or protection request from a station in BSS B cannot reach stations in BSS A and cannot prevent interference due to LRP transmissions from stations in BSS A. LRP transmission from a station in BSS A can be detected at least partially by stations in BSS B but may not cause heavy interference to transmissions from stations in BSS B. If stations in BSS B do not detect heavy NP and/or LRP transmissions in the neighborhood (e.g., if NP and/or LRP transmissions are less than or equal to a predetermined threshold), the stations in BSS B may still access the medium even when a low-rate preamble is detected.

A Network Allocation Vector (NAV) is a virtual carrier sensing mechanism used with wireless network protocols such as IEEE 802.11 and IEEE 802.16 (WiMax). The virtual carrier sensing limits the need for physical carrier sensing to save power. MAC layer frame headers include a duration field that specifies a transmission time required for the frame, in which time the medium will be busy. Stations listening on the medium read the duration field and set their NAV, which indicates to a station how long the station must defer from accessing the medium.

Following are examples of coexistence rules and approaches. Conservatively, if an NP-only device can decode the IR-SIG field of a low-rate packet (i.e., a packet that is transmitted using a LP and that includes a low-rate preamble and data), the NP-only device should defer channel access until the end of the low-rate packet or until the end of the transmission sequence. If the NP-only device can detect LR-STF and/or LR-LTF, but cannot decode the LR-SIG field of a low-rate packet, the NP-only device should defer channel access until the LP-only device correctly decodes a SIG field of a frame (such as a normal-rate packet, which is a packet that is transmitted using a NP and that includes a normal-rate preamble and data). Alternatively, the NP-only device should defer channel access until a frame sequence is detected by which the NP-only device can correctly set its Network Allocation Vector (NAV). Alternatively, the NP-only device should defer channel access until expiration of a predetermined period, such as a maximum possible duration of a low-rate packet or of a single transmission sequence.

To prevent a device from occupying the medium continuously by using short low-rate packets, a duty cycle threshold/limit (e.g., X) can be enforced for the usage of LRP. For example, once a device starts to access the medium successfully, the device can continuously access the medium by using LRP for a maximum period A. After the end of the maximum period A, the device should not access the medium by using LRP for at least a period B. The duty cycle A/(A+B) should be less than or equal to X.

Aggressively, an NP-only station should defer channel access based on a detected LRP transmission only if the LRP transmission is very strong, e.g. greater than or equal to an energy detection threshold (typically 20 dB less than the preamble/STF detection threshold). Using this approach, however, if a dual-PHY station using LRP is close to the NP-only station, the NP-only station may keep ignoring and keep blocking the weak LRP transmissions to the dual-PHY station.

Following are examples of compromise coexistence approaches. An NP-only station should defer channel access based on a detected LRP transmission only if the transmission is stronger than a threshold between the typical energy detection threshold and a preamble/STF detection threshold. The NP-only station should defer the channel access for a predetermined period (such as a maximum low-rate packet period or a maximum transmit opportunity (TXOP) period) unless the NP-only station detects a duration from a detected SIG field or a NAV duration before the end of the predetermined period.

If a dual-PHY station fails to perform a LRP transmission for one or more times, the dual-PHY station may send a special protection request for subsequent LRP transmissions and retransmissions. For example, the dual-PHY station may send the special protection request using a special LR-STF (e.g., a longer LR-STF) for the subsequent retransmissions. When an NP-only station detects the special LR-STF (or special protection request), the NP-only station should defer channel access. If the NP-only station does not detect the special LR-STF (or special protection request), the NP-only station defers channel access only when a transmission stronger than the energy detection threshold is detected.

In some implementations, an NP-only device may be capable of only energy detection. If an NP-only device is unable to detect the LR-STF of any low-rate packet, the NP-only device has to rely on energy detection for channel access and may not be able to detect weak LRP transmissions. To prevent such a NP-only device from accessing the medium by aggressively disregarding the devices using LRP, a duty cycle threshold/limit can be enforced to limit such a NP-only device from accessing a common medium for a long period.

Channel selection may be made as follows. A BSS including NP-only stations should avoid using existing LRP channels as NP primary channel. More generally, once NP-only stations detect LRP transmissions in one channel, the NP-only stations should still be able to use other idle channels for transmissions.

Referring now to FIG. 8, a network device 400 includes a transceiver module 402, a medium access controller (MAC) module 404, and a processor 406. The network device 400 may include an access point (AP) or a client station (STA). The transceiver module 402 includes a physical layer (PHY) module 408 that transmits and receives data via one or more antennas (not shown). Although one PHY module 408 is shown, the transceiver module 402 may include a plurality of PHY modules. The MAC module 404 controls access to medium. The processor 406 processes the data received and to be transmitted by the network device 400.

Referring now to FIGS. 9A and 9B, network devices 500 and 550 are shown, respectively. Each of the network devices 500 and 550 may include an AP or a STA. The network devices 500 and 550 include different PHYs. In FIG. 9A, the network device 500 includes a transceiver module 502. The transceiver module 502 includes a first preamble generation module 504, a second preamble generation module 506, a packet generation module 508, and a PHY module 510. The PHY module 510 may communicate with the medium via one or more antennas (not shown). In FIG. 9B, the network device 550 includes a transceiver module 552. The transceiver module 552 includes the first preamble generation module 504, the second preamble generation module 506, the packet generation module 508, a first PHY module 560, and a second PHY module 562. The PHY modules 560 and 562 may communicate with the medium via one or more antennas (not shown).

The first preamble generation module 504 is configured to generate a first preamble. The first preamble includes a first training field to train receivers operating at a first data rate. For example, the first training field includes a first short training field. Additionally, the first preamble includes a first long training field and a first signal field. The second preamble generation module 506 is configured to generate a second preamble. The second preamble includes a second training field to train receivers operating at a second data rate. For example, the second training field includes a second short training field. Additionally, the second preamble includes a second long training field and a second signal field. The second data rate is different that the first data rate. For example, the first data rate is the normal-rate, and the second data rate is the low-rate. Alternatively, the first data rate is the low-rate, and the second data rate is the normal-rate.

The packet generation module 508 is configured to generate a packet. The packet includes the second preamble followed by the first preamble when the packet is transmitted at the first data rate. Alternatively, the first preamble is followed by the second preamble when the packet is transmitted at the second data rate.

In FIG. 9A, the physical layer module 510 is configured to transmit the packet at the first data rate when the packet includes the second preamble followed by the first preamble. The physical layer module 510 is configured to transmit the packet at the second data rate when the packet includes the first preamble followed by the second preamble. Accordingly, the physical layer module 510 may be called a hybrid physical layer capable of transmitting and receiving a hybrid packet including portions of a first packet generated at the first data rate and a second packet generated at the second data rate.

In FIG. 9B, the first physical layer module 560 is configured to transmit the packet at the first data rate when the packet includes the second preamble followed by the first preamble. The second physical layer module 562 is configured to transmit the packet at the second data rate when the packet includes the first preamble followed by the second preamble.

Referring now to FIG. 10, a client station 600 includes a receiver module 602. The receiver module 602 includes a PHY module 604, a processing module 606, and an energy detection module 608. The PHY module 604 may communicate with the medium via one or more antennas (not shown). In the discussion below, the second data rate is different that the first data rate. For example, the first data rate is the normal-rate, and the second data rate is the low-rate. Alternatively, the first data rate is the low-rate, and the second data rate is the normal-rate.

The physical layer module 604 is configured to receive a packet via the medium. The packet includes a first preamble followed by a second preamble. The first preamble is generated based on a first data rate. The second preamble is generated based on a second data rate. At least one of the first preamble and the second preamble includes a duration of the packet.

The processing module 606 is configured to process the first preamble when the receiver module 602 operates at the first data rate. The processing module 606 is configured to process the second preamble when the receiver module 602 operates at the second data rate. The processing module 606 is configured to determine whether to defer accessing the medium for the duration of the packet based on the processing of the first preamble or the second preamble.

The first preamble includes a first training field (e.g., a first short training field) to train receivers operating at the first data rate and a first signal field to indicate the duration of the packet. The processing module 606 is configured to process the first preamble when the receiver module 602 operates at the first data rate and trains on the first training field. The processing module 606 is configured to determine the duration of the packet based on the first signal field. The processing module 606 is configured to detect an identifier in the first signal field and decide not to access the medium for the duration of the packet when the identifier indicates that the packet is not indented for the receiver module 602.

The second preamble includes a second training field (e.g., a second short training field) to train receivers operating at the second data rate and a second signal field to indicate the duration of the packet. The processing module 606 is configured to process the second preamble when the receiver module 602 operates at the second data rate and trains on the second training field. The processing module 606 is configured to determine the duration of the packet based on the second signal field. The processing module 606 is configured to detect an identifier in the second signal field and decide not to access the medium for the duration of the packet when the identifier indicates that the packet is not indented for the receiver module 602.

When the packet includes data generated at the second rate and the receiver module 602 is configured to operate at the second rate, the processing module 606 is configured to process the first preamble, determine whether the packet includes data generated at the second rate based on the processing of the first preamble, process the second preamble in response to determining that the packet includes data generated at the second rate, and determine the duration of the packet based on the processing of the second preamble. The processing module 602 is configured to detect an identifier in the second preamble and decide not to access the medium for the duration of the packet when the identifier indicates that the packet is not indented for the receiver module 602.

When the packet includes data generated at the first rate and the receiver module 602 is configured to operate at the first rate and the second rate, the processing module 606 is configured to process the first preamble, determine whether the packet includes data generated at the second rate based on the processing of the first preamble, process the second preamble in response to determining that the packet includes data generated at the second rate, and determine the duration of the packet based on the processing of the second preamble. The processing module 606 is configured to detect an identifier in the second preamble and decide not to access the medium for the duration of the packet when the identifier indicates that the packet is not indented for the receiver module 602.

Referring now to FIG. 11, a client station 650 includes a receiver module 652. The receiver module 652 includes a PHY module 654, a midamble detection module 656, a processing module 658, and a power save module 660. The PHY module 654 may communicate with the medium via one or more antennas (not shown). The midamble detection module 656 is configured to detect a midamble of a packet transmitted by a network device via a channel. The packet may include a preamble, a midamble, and a plurality of data fields. The preamble may include a first short training field, a first long training field, and a signal field. The midamble may include a second short training field and a second long training field. The midamble follows the preamble and is between two or more of the data fields (e.g., see FIG. 6). The processing module 658 is configured to determine that the channel is busy when a midamble is detected in the packet.

A midamble may be present in the packet following every predetermined number of data symbols (e.g., after every N data symbols, where N is an integer greater than 1). The power save module 660 is configured to operate the client station 650 in a power save mode for a duration of the predetermined number of data symbols or for a duration of a multiple of the predetermined number of data symbols. The power save module 660 is configured to wake up the client station 650 following the duration. After the client station 650 wakes up, the processing module 658 is configured to determine that the channel is busy if a midamble is detected in the packet. If a midamble is not detected in the packet, the processing module 658 is configured to determine whether the channel is busy based on the preamble.

The physical layer module 654 is configured to communicate at a first data rate via a first sub-channel or via a second sub-channel of the channel. The midamble detection module 656 is configured to detect the midamble in the first sub-channel or in the second sub-channel when the midamble is transmitted at a second data rate via the first sub-channel and the second sub-channel, where the second data rate is greater than the first data rate. For example, the second data rate is the normal-rate, and the first data rate is the low-rate. If the midamble is detected in the first sub-channel or the second sub-channel, the processing module 658 is configured to determine that a transmission at the second data rate is ongoing in the channel and decide not to access the channel.

Referring again to FIG. 10, the physical layer module 604 is configured to communicate at a first data rate via a channel, where the channel includes a first sub-channel and a second sub-channel of the channel. The physical layer module 604 is configured to receive a first packet including a first preamble transmitted at the first data rate via the first sub-channel and the second sub-channel. The physical layer module 604 is configured to receive a second packet including a second preamble transmitted at a second data rate via the first sub-channel or the second sub-channel, where the second data rate is less than the first data rate. For example, the second data rate is the normal-rate, and the first data rate is the low-rate.

The processing module 606 is configured to process the first preamble transmitted at the first data rate and at least a portion of the second preamble transmitted at the second data rate. The processing module 606 is configured to determine that the channel is busy on detecting least the portion of the second preamble transmitted via the first sub-channel or the second sub-channel. The energy detection module 608 is configured to detect an energy level in the channel and determine that the channel is busy when the energy level being greater than or equal to a predetermined threshold.

The first preamble includes a first short training field having a first periodicity and a first remainder (e.g., a long training field and a signal field). The second preamble includes a second short training field having a second periodicity and a second remainder (e.g., a long training field and a signal field). The first remainder is different than the second remainder. The second periodicity is equal to the first periodicity divided by an integer greater than or equal to one. Each of the first short training field and the second short training field activates the processing module 606 (e.g., an autocorrelator in the processing module 606) to process the first preamble transmitted at the first data rate and at least the portion of the second preamble transmitted at the second data rate.

The processing module 606 is configured to process the signal field of the second remainder, determine a duration of the second packet based on processing the signal field of the second remainder, and defer accessing the channel for the duration. The processing module 606 is configured to process the second short training field of the second preamble and the long training field of the second remainder of the second preamble. If the processing module 606 is unable to process the signal field of the second remainder, the processing module 606 is configured to defer accessing the channel until one of the following: the processing module 606 detects a signal field of the first preamble; the processing module 606 detects a frame sequence to set a network allocation vector; or expiration of a predetermined period corresponding to a duration of the second packet or a single transmission sequence.

The processing module 606 is configured to defer accessing the channel for a first predetermined period; access the channel at an end of the first predetermined period; and subsequent to gaining access to the channel at the end of the first predetermined period, access the channel for a second predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle assigned to a device transmitting the second packet. The device accesses the channel during the first predetermined period and does not access the channel during the second predetermined period.

The energy detection module 608 is configured to detect an energy level of the second packet. The processing module 606 is configured to defer accessing the channel if the energy level is greater than or equal to a predetermined threshold. The processing module 606 is configured to defer accessing the channel if the energy level is greater than or equal to a predetermined energy detection threshold and if the energy level is less than or equal to a preamble detection threshold.

The processing module 606 is configured to defer accessing the channel for a predetermined period unless the processing module 606 detects, prior to expiration of the predetermined period, a duration of the first packet or the second packet respectively from a signal field of the first preamble or the second preamble or a network allocation vector duration.

The second preamble includes a short training field and may be transmitted by a device configured to transmit the first preamble via the channel at the first data rate and the second preamble via the first sub-channel or the second sub-channel at the second data rate. A length of the short training field in the second preamble may be increased if a transmission from the device at the second rate fails a plurality of times. The energy detection module 608 is configured to detect an energy level of the second packet. The processing module 606 is configured to defer accessing the channel on detecting the short training field having the increased length. Alternatively, the processing module 606 is configured to defer accessing the channel if the energy level is greater than or equal to a predetermined threshold and if the short training field having the increased length is not detected.

The processing module 606 is configured to defer accessing the channel if the energy level is greater than or equal to a predetermined threshold and id the second preamble is not detected. Subsequent to gaining access to the channel based on the energy level, the processing module 606 is configured to access the channel for a first predetermined period. The processing module 606 is configured to stop accessing the channel after expiration of the first predetermined period. The processing module 606 is configured to not access the channel for a second predetermined period following the expiration of the first predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle.

Referring again to FIG. 9B, the network device 550 may include an access point (AP). The first physical layer module 560 is configured to communicate at a first data rate via a first sub-channel and a second sub-channel of a channel. The second physical layer module 562 is configured to communicate at a second data rate via the first sub-channel or the second sub-channel. The first data rate is greater than the second data rate. For example, the first data rate is the normal-rate, and the second data rate is the low-rate.

The first physical layer module 560 is configured to receive a request from a first client station (e.g., station STA2 204 in FIG. 3) to reserve the channel for transmitting data from the first client station to the access point at the first data rate. The request is not received by a second client station (e.g., station STA1 202 in FIG. 3) configured to transmit data to the access point via the first sub-channel or the second sub-channel at the second rate.

In response to receiving the request from the first client station, the access point is configured to transmit a response to allow the first client station to transmit data via the channel and to prevent the second client station from transmitting data via the first sub-channel or the second sub-channel while the first client station transmits data to the access point via the channel.

When the first client station receives the response, the first physical layer module 562 is configured to receive data from the first client station without interference from the second client station. The request and the response may be of different types and may be transmitted in different ways as follows.

For example, the request may include a ready-to-send frame, and the response may include a clear-to-send frame. The first physical layer module 560 and the second physical layer module 562 may send the clear-to-send frame.

The first physical layer module 560 may transmit the response prior to the second physical layer module 562 transmitting the response, and the second physical layer module 562 may transmit the response subsequent to the first physical layer module 560 transmitting the response. Alternatively, the second physical layer module 562 may transmit the response prior to the first physical layer module 560 transmitting the response, and the first physical layer module 560 may transmit the response subsequent to the second physical layer module 562 transmitting the response.

The response may include a hybrid packet, where the hybrid packet includes a first preamble generated at the first data rate, a second preamble generated at the second data rate, and a payload generated at the second data rate. The first preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a hybrid packet, where the hybrid packet includes a first preamble generated at the second data rate, a second preamble generated at the first data rate, and a payload generated at the first data rate. The first preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a first packet followed by a gap and a second packet. The first packet may be generated at the first data rate. The second packet may be generated at the second data rate. The second packet may include no payload (i.e., the second packet may be a no data packet or NDP) and a preamble. The preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a first packet followed by a gap and a second packet. The first packet may be generated at the second data rate. The second packet may be generated at the first data rate. The second packet may include no payload (i.e., the second packet may be a no data packet or NDP) and a preamble. The preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

Referring again to FIG. 9B, the network device 550 may include an access point (AP). The first physical layer module 560 is configured to communicate at a first data rate via a first sub-channel and a second sub-channel of a channel. The second physical layer module 562 is configured to communicate at a second data rate via the first sub-channel or the second sub-channel. The first data rate is greater than the second data rate. For example, the first data rate is the normal-rate, and the second data rate is the low-rate.

The second physical layer module 562 is configured to receive a request from a first client station (e.g., station STA1 202 in FIG. 3) to reserve the first sub-channel or the second sub-channel for transmitting data from the first client station to the access point at the second data rate. The request cannot be processed by a second client station (e.g., station STA2 204 in FIG. 3) configured to transmit data to the access point via channel at the first rate.

In response to receiving the request from the first client station, the access point is configured to transmit a response to allow the first client station to transmit data via the first sub-channel or the second sub-channel and prevent the second client station from transmitting data via the channel while the first client station transmits data to the access point via the first sub-channel or the second sub-channel.

When the first client station receives the response, the first physical layer module 562 is configured to receive data from the first client station without interference from the second client station. The request and the response may be of different types and may be transmitted in different ways as follows.

For example, the request may include a ready-to-send frame, and the response may include a clear-to-send frame. The first physical layer module 560 and the second physical layer module 562 may send the clear-to-send frame.

The first physical layer module 560 may transmit the response prior to the second physical layer module 562 transmitting the response, and the second physical layer module 562 may transmit the response subsequent to the first physical layer module 560 transmitting the response. Alternatively, the second physical layer module 562 may transmit the response prior to the first physical layer module 560 transmitting the response, and the first physical layer module 560 may transmit the response subsequent to the second physical layer module 562 transmitting the response.

The response may include a hybrid packet, where the hybrid packet includes a first preamble generated at the first data rate, a second preamble generated at the second data rate, and a payload generated at the second data rate. The first preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a hybrid packet, where the hybrid packet includes a first preamble generated at the second data rate, a second preamble generated at the first data rate, and a payload generated at the first data rate. The first preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a first packet followed by a gap and a second packet. The first packet may be generated at the first data rate. The second packet may be generated at the second data rate. The second packet may include no payload (i.e., the second packet may be a no data packet or NDP) and a preamble. The preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

The response may include a first packet followed by a gap and a second packet. The first packet may be generated at the second data rate. The second packet may be generated at the first data rate. The second packet may include no payload (i.e., the second packet may be a no data packet or NDP) and a preamble. The preamble may include a duration for which the channel is reserved for the first client station to transmit data to the access point.

Referring again to FIGS. 3 and 9B, a first client station (e.g., station STA1 202 in FIG. 3) may communicate with an access point (e.g., the AP 200 in FIG. 3) in presence of a second client station (e.g., station STA2 204 in FIG. 3) as follows. The AP 200 may include the network device 550 of FIG. 9B. The first client station may also include the network device 550 of FIG. 9B. The second client station may be capable of communicating at a first data rate (e.g., the normal-rate).

The first client station may include a first physical layer module (e.g., 560) configured to communicate at the first data rate via a first sub-channel and a second sub-channel of a channel. The first client station may include a second physical layer module (e.g., 562) configured to communicate at a second data rate (e.g., the low-rate) via the first sub-channel or the second sub-channel. The first data rate is greater than the second data rate. The first client station is configured to communicate with the access point that is associated with the second client station.

The first client station is configured to transmit a request to the access point to reserve the channel for transmitting data at the first data rate or to reserve the first sub-channel or the second sub-channel for transmitting data at the second data rate. The first client station is also configured to transmit data to the access point without interference from the second client station. The first client station is configured to transmit the request and the data using one of the following: the second physical layer module only; the first physical layer module and the second physical layer module; transmission of a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the first packet includes no payload and includes a preamble, and where the second packet is generated at the second data rate and includes payload; or transmission of the second packet followed by the gap and the first packet.

The access point is configured to transmit a response to allow the first client station to transmit data using the first physical layer module via the channel or using the second physical layer module via the first sub-channel or the second sub-channel and prevent the second client station from transmitting data via the channel while the first client station transmits data to the access point.

The access point includes a first physical layer module (e.g., 560) configured to communicate at the first data rate via the first sub-channel and the second sub-channel. The access point may include a second physical layer module (e.g., 562) configured to communicate at the second data rate via the first sub-channel or the second sub-channel. The access point transmits the response using one of the following: the second physical layer module only; the first physical layer module and the second physical layer module; transmission of a first packet followed by the gap and a second packet, where the first packet is generated at the first data rate, where the first packet includes no payload and includes a preamble, where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point, and where the second packet is generated at the second data rate and includes payload; or transmission of the second packet followed by the gap and the first packet.

Referring now to FIG. 12, a method 700 for transmitting a packet according to the present disclosure is shown. At 702, control generates a first preamble including a first training field to train receivers operating at a first data rate. At 704, control generates a second preamble including a second training field to train receivers operating at a second data rate, where the second data rate is different than the first data rate. At 706, control transmits a packet including the second preamble followed by the first preamble if the packet is transmitted at the first data rate. At 708, control transmits a packet including the first preamble followed by the second preamble if the packet is transmitted at the second data rate.

Referring now to FIGS. 13A and 13B, a method 800 for processing a received packet according to the present disclosure is shown. At 802, control receives a packet at a receiver, where the packet includes a first preamble followed by a second preamble, the first preamble is generated based on a first data rate, the second preamble is generated based on a second data rate, and at least one of the first preamble and the second preamble includes a duration of the packet. At 804, control processes the first preamble if the receiver operates at the first data rate or the second preamble if the receiver operates at the second data rate, and control determines whether to defer accessing the medium for the duration of the packet based on the processing of the first preamble or the second preamble.

At 806, the first preamble includes a first training field to train receivers operating at the first data rate and a first signal field to indicate the duration of the packet, and control processes the first preamble if the receiver operates at the first data rate and trains on the first training field, and determines the duration of the packet based on the first signal field. Control detects an identifier in the first signal field and decides not to access the medium for the duration of the packet if the identifier indicates that the packet is not indented for the receiver.

At 808, the second preamble includes a second training field to train receivers operating at the second data rate and a second signal field to indicate the duration of the packet, and control processes the second preamble if the receiver operates at the second data rate and trains on the second training field, and determines the duration of the packet based on the second signal field. Control detects an identifier in the second signal field and decides not to access the medium for the duration of the packet if the identifier indicates that the packet is not indented for the receiver.

At 810, if the packet including data generated at the second rate and the receiver is configured to operate at the second rate, control processes the first preamble, and determines whether the packet includes data generated at the second rate based on the processing of the first preamble. Control processes the second preamble in response to determining that the packet includes data generated at the second rate, and determines the duration of the packet based on the processing of the second preamble. Control detects an identifier in the second preamble and decides not to access the medium for the duration of the packet if the identifier indicates that the packet is not indented for the receiver.

At 812, if the packet includes data generated at the first rate and the receiver is configured to operate at the first rate and the second rate, control processes the first preamble, determines whether the packet includes data generated at the second rate based on the processing of the first preamble. Control processes the second preamble in response to determining that the packet includes data generated at the second rate, and determines the duration of the packet based on the processing of the second preamble. Control detects an identifier in the second preamble and decides not to access the medium for the duration of the packet if the identifier indicates that the packet is not indented for the receiver.

Referring now to FIGS. 14A and 14B, a method 850 for solving the hidden terminal problem according to the present disclosure is shown. At 852, control communicates at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of an access point. Control communicates at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the access point, where the first data rate is greater than the second data rate. Control receives at the first physical layer module, from a first client station, a request to reserve the channel for transmitting data from the first client station to the access point at the first data rate, where the request is not received by a second client station configured to transmit data to the access point via the first sub-channel or the second sub-channel at the second rate. In response to the first physical layer module receiving the request from the first client station, control transmits a response from the access point to (i) allow the first client station to transmit data at the first data rate via the channel, and (ii) prevent the second client station from transmitting data via the first sub-channel or the second sub-channel at the second rate while the first client station transmits data at the first data rate to the access point via the channel.

At 854, the request includes a ready-to-send frame, the response includes a clear-to-send frame, and control sends the clear-to-send frame via the first physical layer module and the second physical layer module.

At 856, control transmits the response from the first physical layer module prior to the second physical layer module transmitting the response, and control transmits the response from the second physical layer module subsequent to the first physical layer module transmitting the response; or control transmits the response from the second physical layer module prior to the first physical layer module transmitting the response, and control transmits the response from the first physical layer module subsequent to the second physical layer module transmitting the response.

At 858, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 860, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 862, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 864, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 866, in response to the first client station receiving the response, control receives data at the first physical layer module from the first client station without interference from the second client station.

Referring now to FIGS. 15A and 15B, a method 900 for solving the coexistence problems according to the present disclosure is shown. At 902, control communicates at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of an access point. Control communicates at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the access point, where the first data rate is greater than the second data rate. Control receives at the second physical layer module, from a first client station, a request to reserve the first sub-channel or the second sub-channel for transmitting data from the first client station to the access point at the second data rate, where the request is not processed by a second client station configured to transmit data to the access point via the channel at the first rate. In response to the second physical layer module receiving the request from the first client station, control transmits a response from the access point to (i) allow the first client station to transmit data at the second data rate via the first sub-channel or the second sub-channel, and (ii) prevent the second client station from transmitting data at the first data rate via the channel while the first client station transmits data at the second data rate to the access point via the first sub-channel or the second sub-channel.

At 904, the request includes a ready-to-send frame, where the response includes a clear-to-send frame, and where the first physical layer module and the second physical layer module send the clear-to-send frame.

At 906, control transmits the response from the first physical layer module prior to the second physical layer module transmitting the response, and control transmits the response from the second physical layer module subsequent to the first physical layer module transmitting the response; or control transmits the response from the second physical layer module prior to the first physical layer module transmitting the response, and control transmits the response from the first physical layer module subsequent to the second physical layer module transmitting the response.

At 908, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the first data rate, (ii) a second preamble generated at the second data rate, and (iii) a payload generated at the second data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 910, the response includes a hybrid packet, where the hybrid packet includes (i) a first preamble generated at the second data rate, (ii) a second preamble generated at the first data rate, and (iii) a payload generated at the first data rate, and where the first preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 912, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate, where the second packet is generated at the second data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 914, the response includes a first packet followed by a gap and a second packet, where the first packet is generated at the second data rate, where the second packet is generated at the first data rate, where the second packet includes (i) no payload and (ii) a preamble, and where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point.

At 916, in response to the first client station receiving the response, control receives data at the second physical layer module from the first client station without interference from the second client station.

Referring now to FIG. 16, a method 950 for solving the coexistence problem according to the present disclosure is shown. At 952, control communicates at a first data rate via a first sub-channel and a second sub-channel of a channel using a first physical layer module of a first client station. Control communicates at a second data rate via (i) the first sub-channel or (ii) the second sub-channel using a second physical layer module of the first client station, where the first data rate is greater than the second data rate, and where the first client station is configured to communicate with an access point associated with a second client station capable of communicating at the first data rate. Control transmits from the first client station (i) a request to the access point to reserve the channel for transmitting data at the first data rate or to reserve the first sub-channel or the second sub-channel for transmitting data at the second data rate and (ii) data to the access point without interference from the second client station, using (i) the second physical layer module only, (ii) the first physical layer module and the second physical layer module, (iii) transmission of a first packet followed by a gap and a second packet, where the first packet is generated at the first data rate and includes no payload, and where the second packet is generated at the second data rate and includes payload, or (iv) transmission of the second packet followed by the gap and the first packet.

At 954, control transmits from the access point a response to (i) allow the first client station to transmit data using the first physical layer module via the channel or using the second physical layer module via the first sub-channel or the second sub-channel and (ii) prevent the second client station from transmitting data via the channel while the first client station transmits data to the access point.

At 956, control communicates at the first data rate via the first sub-channel and the second sub-channel using a third physical layer module of the access point. Control communicates at the second data rate via (i) the first sub-channel or (ii) the second sub-channel using a fourth physical layer module of the access point. Control transmits the response from the access point using (i) the fourth physical layer module only, (ii) the third physical layer module and the fourth physical layer module, (iii) transmission of a third packet followed by the gap and a fourth packet, where the third packet is generated at the first data rate and includes no payload and a preamble, where the preamble includes a duration for which the channel is reserved for the first client station to transmit data to the access point, and where the fourth packet is generated at the second data rate and includes payload, or (iv) transmission of the fourth packet followed by the gap and the third packet.

Referring now to FIGS. 17A-17C, a method 1000 for coexistence of devices having varying capabilities according to the present disclosure is shown. At 1002, control communicates at a first data rate via a channel using a physical layer module, where the channel includes (i) a first sub-channel and (ii) a second sub-channel of the channel. Control receives, using the physical layer module, a first packet including a first preamble transmitted at the first data rate via (i) the first sub-channel and (ii) the second sub-channel. Control receives, using the physical layer module, a second packet including a second preamble transmitted at a second data rate via (i) the first sub-channel or (ii) the second sub-channel, where the second data rate is less than the first data rate. Control processes (i) the first preamble transmitted at the first data rate and (ii) at least a portion of the second preamble transmitted at the second data rate.

At 1004, control determines that the channel is busy in response to detecting at least the portion of the second preamble transmitted via (i) the first sub-channel or (ii) the second sub-channel.

At 1006, control detects an energy level in the channel and determines that the channel is busy in response to the energy level being greater than or equal to a predetermined threshold.

At 1008, the first preamble includes (i) a first short training field having a first periodicity and (ii) a first remainder, the second preamble includes (i) a second short training field having a second periodicity and (ii) a second remainder, the second periodicity is equal to the first periodicity divided by an integer greater than or equal to one, and the first remainder is different than the second remainder.

At 1010, each of the first short training field and the second short training field activates the processing of (i) the first preamble transmitted at the first data rate and (ii) at least a portion of the second preamble transmitted at the second data rate.

At 1012, the second remainder includes a signal field, and control processes the signal field; determines a duration of the second packet based on processing the signal field; and defers accessing the channel for the duration.

At 1014, the second remainder includes (i) a long training field and (ii) a first signal field, and control processes (i) the second short training field and (ii) the long training field. In response to inability to process the first signal field, control defers accessing the channel until (i) detecting a second signal field of the first preamble, (ii) detecting a frame sequence to set a network allocation vector, or (iii) expiration of a predetermined period corresponding to a duration of the second packet or a single transmission sequence.

At 1016, control defers accessing the channel for a first predetermined period, accesses the channel at an end of the first predetermined period, and subsequent to gaining access to the channel at the end of the first predetermined period, accesses the channel for a second predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle assigned to a device transmitting the second packet. The device accesses the channel during the first predetermined period and does not access the channel during the second predetermined period.

At 1018, control detects an energy level of the second packet, and defers accessing the channel in response to the energy level being greater than or equal to a predetermined threshold.

At 1020, control detects an energy level of the second packet, and defers accessing the channel in response to the energy level being (i) greater than or equal to a predetermined energy detection threshold and (ii) less than or equal to a preamble detection threshold.

At 1022, control defers accessing the channel for a predetermined period unless, prior to expiration of the predetermined period, (i) duration of the first packet or the second packet is detected respectively from a signal field of the first preamble or the second preamble or (ii) network allocation vector duration is detected.

At 1024, the second preamble includes a short training field and is transmitted by a device configured to transmit (i) the first preamble via the channel at the first data rate and (ii) the second preamble via the first sub-channel or the second sub-channel at the second data rate, and a length of the short training field is increased in response to a transmission from the device at the second rate failing a plurality of times. Control detects an energy level of the second packet, and defers accessing the channel in response to detecting the short training field having an increased length, or (i) the energy level being greater than or equal to a predetermined threshold and (ii) the short training field having the increased length not being detected.

At 1026, control detects an energy level of the second packet, defers accessing the channel in response to (i) the energy level being greater than or equal to a predetermined threshold and (ii) the second preamble being not detected, and subsequent to gaining access to the channel based on the energy level, (i) accesses the channel for a first predetermined period, (ii) stops accessing the channel after expiration of the first predetermined period, and (iii) does not access the channel for a second predetermined period following the expiration of the first predetermined period. The first predetermined period and the second predetermined period are based on a predetermined duty cycle.

Referring now to FIG. 18, a method 1050 for coexistence of a normal-rate physical layer and a low-rate physical layer in a wireless network using midambles according to the present disclosure is shown. At 1052, control detects a midamble of a packet transmitted via a channel, where the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, where the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, where the midamble includes (i) a second short training field and (ii) a second long training field, and where the midamble follows the preamble and is between two or more of the data fields. Control determines that the channel is busy in response to detecting the midamble in the packet.

At 1054, in response to the midamble being present in the packet following every predetermined number of data symbols, control operates a client station in a power save mode for a duration of (i) the predetermined number of data symbols or (ii) a multiple of the predetermined number of data symbols; wakes up the client station following the duration; and determines, subsequent to the client station waking up, that the channel is busy in response to detecting the midamble in the packet.

At 1056, in response the midamble not being detected in the packet, control determines whether the channel is busy in response to detecting the preamble.

At 1058, control communicates at a first data rate via (i) a first sub-channel or (ii) a second sub-channel of the channel using a physical layer module; detects the midamble in (i) the first sub-channel or (ii) the second sub-channel in response to the midamble being transmitted at a second data rate via (i) the first sub-channel and (ii) the second sub-channel, where the second data rate is greater than the first data rate; and determines, in response to the midamble being detected in (i) the first sub-channel or (ii) the second sub-channel, that a transmission at the second data rate is ongoing in the channel, and deciding not to access the channel.

The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical OR. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure.

As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor.

The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors. In addition, some or all code from a single module may be stored using a group of memories.

The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. 

What is claimed is:
 1. A client station comprising: a receiver physical layer module configured to communicate at a first data rate via (i) a first sub-channel or (ii) a second sub-channel of a channel; a receiver midamble detection module configured to detect a midamble of a packet transmitted via the channel, wherein the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, wherein the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, wherein the midamble includes (i) a second short training field and (ii) a second long training field, and wherein the midamble follows the preamble and is between two or more of the data fields; and detect the midamble in (i) the first sub-channel or (ii) the second sub-channel in response to the midamble being transmitted at a second data rate via (i) the first sub-channel and (ii) the second sub-channel, wherein the second data rate is greater than the first data rate; and a receiver processing module is configured to determine, in response to the midamble being detected in (i) the first sub-channel or (ii) the second sub-channel, that a transmission at the second data rate is ongoing in the channel, and determine, in response to the midamble not being detected in the packet, whether the channel is busy in response to detecting the preamble, wherein responsive to the channel being determined to be busy, the receiver processing module decides not to access the channel.
 2. The client station of claim 1, wherein in response to the midamble being present in the packet following every predetermined number of data symbols, the client station further comprising: a receiver power save module configured to operate the client station in a power save mode for a duration of (i) the predetermined number of data symbols or (ii) a multiple of the predetermined number of data symbols, and wake up the client station following the duration, wherein the receiver processing module is configured to determine, subsequent to the client station waking up, that the channel is busy in response to detecting the midamble in the packet.
 3. A method comprising: communicating at a first data rate via (i) a first sub-channel or (ii) a second sub-channel of a channel using a physical layer module; detecting a midamble of a packet transmitted via the channel, wherein the packet includes (i) a preamble, (ii) the midamble, and (iii) a plurality of data fields, wherein the preamble includes (i) a first short training field, (ii) a first long training field, and (iii) a signal field, wherein the midamble includes (i) a second short training field and (ii) a second long training field, and wherein the midamble follows the preamble and is between two or more of the data fields; detecting the midamble in (i) the first sub-channel or (ii) the second sub-channel in response to the midamble being transmitted at a second data rate via (i) the first sub-channel and (ii) the second sub-channel, wherein the second data rate is greater than the first data rate; determining, in response to the midamble being detected in (i) the first sub-channel or (ii) the second sub-channel, that a transmission at the second data rate is ongoing in the channel; determining, in response to the midamble not being detected in the packet, whether the channel is busy in response to detecting the preamble; and deciding, responsive to the channel being determined to be busy, not to access the channel.
 4. The method of claim 3, wherein in response to the midamble being present in the packet following every predetermined number of data symbols, the method further comprising: operating a client station in a power save mode for a duration of (i) the predetermined number of data symbols or (ii) a multiple of the predetermined number of data symbols; waking up the client station following the duration; and determining, subsequent to the client station waking up, that the channel is busy in response to detecting the midamble in the packet. 